Heat oil in a large ovenproof pot over high. Cook chuck roast, turning occasionally, until browned on both sides, 3 minutes per side.
Transfer to a plate.
Cook the onion, peppers, stirring occasionally, until softened.
Add garlic and cook, stirring frequently and scraping bottom of pan, until vegetables are golden brown.
Deglaze with a dash vinegar.
Stir in the stock and cook, stirring occasionally,
Stir in paprika, oregano, cumin, black pepper, and cayenne until vegetables are coated; continue to cook, stirring, until spices are fragrant, about 1 minute. Add tomatoes and coarsely break up with a spoon (they’ll continue to break down as they cook).
Bring to a boil and cook, stirring occasionally, until liquid is reduced by half, about 5 minutes.
Cover and transfer to oven. cook until meat is very tender and shreds easily, 2½–3 hours. Let cool 15 minutes.